Molecular Dynamics Insight into the CO2 Flooding Mechanism in Wedge-Shaped Pores

Abstract

Because of the growing demand for energy, oil extraction under complicated geological conditions is increasing. Herein, oil displacement by CO2 in wedge-shaped pores was investigated by molecular dynamics simulation. The results showed that, for both single and double wedge-shaped models, pore Ⅱ (pore size from 3 to 8 nm) exhibited a better CO2 flooding ability than pore Ⅰ (pore size from 8 to 3 nm). Compared with slit-shaped pores (3 and 8 nm), the overall oil displacement efficiency followed the sequence of 8 nm > double pore Ⅱ > single pore Ⅱ > 3 nm > double pore Ⅰ > single pore Ⅰ, which confirmed that the exits of the wedge-shaped pores had determinant effects on CO2 enhanced oil recovery over their entrances. “Oil/CO2 inter-pore migration” and “siphoning” phenomena occurred in wedge-shaped double pores by comparing the volumes of oil/CO2 and the center of mass. The results of the interaction and radial distribution function analyses indicate that the wide inlet and outlet had a larger CO2–oil contact surface, better phase miscibility, higher interaction, and faster displacement. These findings clarify the CO2 flooding mechanisms in wedge-shaped pores and provide a scientific basis for the practical applications of CO2 flooding.

Study on the Effects of Wettability and Pressure in Shale Matrix Nanopore Imbibition during Shut-in Process by Molecular Dynamics Simulations

“…The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/molecules29051112/s1, Figure S1: The interaction energy between oil and wall during structural optimization of the oil-pore systems of imbibition systems I and II; Figure S2 S1: The average mass fraction of light, heavy, and medium hydrocarbon components of the Jimsar shale oil; Table S2: The mole fractions and number of each component of the shale oil model; Table S3: Atomic charge and detailed interaction parameter of SiO 2 , oil, and water. References [59,63,85,86] are cited in the Supplementary Materials.…”

“…(d) Static wetting angle of W A and W B ; Figure S6: The mass fraction of hydrocarbons with different numbers of carbon atoms of (a) JHW05815 Oil Sample, (b) JHW07121 Oil Sample, and (c) J41 Oil Sample; Table S1: The average mass fraction of light, heavy, and medium hydrocarbon components of the Jimsar shale oil; Table S2: The mole fractions and number of each component of the shale oil model; Table S3: Atomic charge and detailed interaction parameter of SiO 2 , oil, and water. References [ 59 , 63 , 85 , 86 ] are cited in the Supplementary Materials.…”

Exploration of Oil/Water/Gas Occurrence State in Shale Reservoir by Molecular Dynamics Simulation

“…The α-quartz was obtained from the Materials Studio 2018 (MS) software database and cut along the (010) crystal direction to form a rock surface [33][34][35]. The size of the rock is 200.0 Å × 29.5 Å × 14.1 Å. Hydroxylation of the rock surface was achieved by attaching an H atom to each O atom on the surface [36], making it hydrophilic and consistent with actual shale pore conditions. The surface density of hydroxyl groups after hydroxylation was 9.6 nm −2 , which is similar to the result determined by crystal chemistry (5.9-18.8 nm −2 ) [37].…”

Molecular Insights into Soaking in Hybrid N2–CO2 Huff-n-Puff: A Case Study of a Single Quartz Nanopore-Hydrocarbon System

“…Thus, the simulated results of the soaking model composed of the dead-end pore may not precisely match the actual HnP/soaking situation. It is worth noting that existing MD simulation studies of gas injection displacement driven by external pressure differences often use the through-hole model, − which is ordinary and reasonable. However, the previous MD simulation studies of the gas injection HnP/soaking process focus on dead-end pores, which are not entirely consistent with natural reservoir conditions.…”

“…Figure 4 shows that the density of the hydrocarbon and CO 2 adsorption layers are characterized by faster changes relative to the bulk density, representing a quicker migration of CO 2 near the quartz wall surface than bulk CO 2 during the soaking process because the steric hindrance between hydrocarbon molecules in the center of the pore 41 and strong adsorption of CO 2 by quartz walls. 39,74 Therefore, the rapid adsorption advancement of CO 2 on the wall surface results in rapid desorption of hydrocarbon molecules from the pore walls. After about T = 7 ns, the peak density of first adsorption layer of hydrocarbon molecules in Figure 4a almost completely disappeared, and hydrocarbon molecules near the wall and in the pore center have similar density values.…”